pfSense

Entering a host name with a "-" in it gives a generic "Please match the requested format" error, for the "TFTP Server" field on the DHCP Server configuration page. It should be considered a legitimate character.

(Pedantically, maybe it's the "dash" or "endash" or "minus sign" character? Not sure. Same key as the underscore on a US keyboard, though it's probably already clear what it is.)